The present invention relates to an internal-combustion engine, and more particularly, to a diesel engine with an exhaust-gas filter arranged in the exhaust pipe in which an exhaust gas recirculating line having an exhaust gas recirculating control valve leads from the exhaust pipe to the intake pipe, with the exhaust gas recirculating control valve acted upon by a control signal for the control of a recirculated exhaust gas quantity.
German Pat. No. DE-OS 25 19 609 shows an internal-combustion engine measuring device arranged in the bypass pipe. This device determines the pressure of the exhaust gases in the sections of the exhaust pipe situated upstream and downstream of the exhaust gas filter as the differential pressure which, as the measuring signal, is guided to a control unit to initiate regeneration of the exhaust gas filter when a given differential pressure is reached. A disadvantage of the known measuring device is that it can be used only for initiating the regenerating of the exhaust gas filter.
In addition, a diesel internal-combustion engine is shown in German Pat. No. DE-OS 32 35 953 and has an exhaust gas filter in the exhaust pipe as well as a bypass pipe for the bypassing of exhaust gas at the exhaust gas filter, with the bypass line controlled by a bypass valve. In addition, this diesel internal-combustion engine also has an exhaust gas recirculating system with an exhaust gas recirculation valve. The bypass valve and the exhaust gas recirculating valve are controlled such that they are open in the partial-load operation and closed in the full-load operation. A control of the recirculated exhaust gas quantity as a function of the charge condition of the exhaust gas filter is not provided.
It is an object of the present invention to further improve a measuring device such that, on one hand, in the operating ranges with exhaust gas recirculation, an exhaust gas recirculation rate adapted to the operating conditions of the internal-combustion engine as precisely as possible can be maintained, and, on the other hand, an operation of the internal-combustion engine is still reliably ensured even when the exhaust gas filter is completely or predominantly clogged.
This object has been achieved in accordance with the present invention by the provision of an exhaust gas recirculating line having an exhaust gas recirculating line with an exhaust gas recirculating control valve which leads from the exhaust pipe to the intake pipe. The exhaust gas recirculating control valve, from the control unit, is acted upon by a control signal for the control of a recirculated exhaust gas quantity which is a function of the differential pressure, with the control signal derived from the measuring signal of the control piston. Starting from a given differential pressure, the control piston opens up a bypass duct so that a partial flow from the section of the exhaust pipe situated upstream of the exhaust gas filter can flow through the bypass line.
The measuring device in accordance with the invention is constructed such that it operates as pressure measuring device until an adjustable upper differential pressure is reached. For this function, only an extremely small quantity of exhaust gas may flow around the piston of this measuring device which is subjected to the differential pressure. This flowing-around is a function of the installation of an exhaust gas turbocharger upstream or downstream of the exhaust gas filter in the exhaust pipe. However, the exhaust gas quantity flowing around the piston is so small that it is negligible with respect to the function of the exhaust gas filter and to the purification of the exhaust gases from carbon particles that can be achieved thereby. The position of the piston subjected to the differential pressure, which is proportional to the respective differential pressure, inside the housing can be detected by a displacement meter via a rod connected directly to the piston. The differential pressure thus detected is used as, inter alia, a controlled variable for automatically controlling the exhaust mass flow to be recirculated for combustion. Further controlled variables dependent on engine operation may also be used, as superimposed variables, for automatically controlling the exhaust mass flow to be recirculated.
In the event of an unwanted clogging of the exhaust-gas filter and also in the event of an undesirably temporarily high pressure loss in the exhaust-gas filter, the present invention provides that the exhaust can flow automatically past the exhaust-gas filter via a bypass.
The measuring device according to the present invention is thus set up such that, when a predeterminable pressure loss at the exhaust-gas filter is exceeded, the exhaust bypass flow, which is flowing in the measuring instrument determining the pressure drop in the exhaust-gas filter and in itself is quantitatively negligible, increases abruptly, to be precise to such an extent that virtually the entire exhaust can flow temporarily in the exhaust-gas bypass filter. If the measuring instrument has assumed such a function, it has in this state lost its function as a pressure-difference measuring device. The displacement meter connected to the piston of the measuring device subjected to the differential pressure detects the change in function of the measuring instrument into an exhaust bypass line and can in such a case reduce or even completely prevent the exhaust gas recirculation.
With an increased flow resistance of, in particular, a soot burn-off filter of a diesel engine, in many cases such a reduction or prevention of the exhaust gas recirculation is desired, in order to prevent already in the state of an increasing flow resistance any further increase by reducing or preventing the quantity of exhaust gas recirculated. An exhaust gas recirculation mainly has the effect of reducing the oxygen content in the exhaust, whereby a burning-off of soot in the exhaust-gas filter is made additionally more difficult, with the consequence that the burn-off behavior becomes worse and worse due to the lower oxygen content, with the consequence that the filter may block entirely if unfavorable operating conditions persist.